Image data obtained or to be obtained with a digital still camera is different from a photograph taken with a conventional silver-film camera. Various digital image processes may be applied to the image data of the digital still camera.
For example, according to one of the digital image processes, or one of the functions of the digital still camera, the image data obtained with the digital still camera is processed as follows. A first photograph of a fixed subject A and a person B is taken with a picture composition which includes the fixed subject A at the center of a frame FL and the person B at a right side of the frame FL, as shown in FIG. 9A.
A second photograph of subjects C and A is taken with a picture composition similar to the first photograph, which includes the subject C at the left side of the frame FL as shown in FIG. 9B.
When the second photograph is taken, the image of the first photograph is displayed on a liquid crystal display panel of the digital camera, more specifically, the image of the fixed subject A and the person B in the first photograph shown in FIG. 9A is displayed in a right two-thirds area of the frame FL of the liquid crystal display panel in a semi-transparent state. Therefore, if the second photograph is taken with the current subject A overlapping precisely with the subject A of the first photograph, second image data shown in FIG. 9B is obtained, which is used to be combined with the first image data shown in FIG. 9A, providing image data as shown in FIG. 9C. The combination of the first and the second image data obtained as set forth above produces a resultant image data, which shows the subjects A and C, as if they are photographed together although actually they are photographed separately.
Since the digital camera has the image composing function set forth above, image data of two persons B and C shown in FIG. 9C may be obtained by photographing the persons B and C separately and combining the separately obtained image data of the persons B and C without using a tripod and a self timer function or without asking other person to take their picture.
To obtain the same image quality as the first photograph, the second photograph must be taken under substantially the same photographing conditions for the first photograph, such as the zoom position of a zoom lens, exposure conditions including focus and shutter speed, white balance, and flash setting.
In the above mentioned image composing procedure, two sets of image data are combined, but an arbitrary number of sets of image data may be combined in a similar manner.
Regarding the image composing technique, there has been proposed a technique of combining image data and other image data including a series of characters, in which a tilt of the characters are corrected prior to be combined with the former image data. (Refer to Japanese laid-open patent application No. H8-065457)
Further, another image composing technique has been proposed, in which image data captured with plural cameras installed on a moving body and the image data are corrected based on angles and a movement detected from the moving body prior to being subjected to the combination process. (Refer to Japanese laid-open patent application No. 2001-245131)
However, in the conventional technique described with reference to FIGS. 9A, 9B, 9C and 9D, image data are acquired with an unfixed camera separately by separate persons, and therefore the image data can be acquired with a slightly changed camera angle. If these image data are combined, the resultant image data will produce an unnatural feeling compared with image data which is obtained by photographing two persons together.
FIG. 9D is a view showing a sample of the combined image data, in which the subject C of the second image data has a tilt to the left compared with the subjects A and B in the first image data. This is caused by the tilted camera angle of the camera at which the second photograph is taken.
The technique disclosed in Japanese laid-open patent application No. H8-065457 can not be used for the correcting the camera angle, because this technique is for correcting the tile of the series of characters.
The technique disclosed in Japanese laid-open patent application No. 2001-245131 is for detecting a tilt of a camera using a gyroscope to compose image data and may be used for a moving body such as an automobile and a train, but it is not practical to use the technique for a compact device such as a digital camera and a cellular phone.